Cranberry  Side Effects

Cranberries are the fruit of a plant that's native to North America. Evidence to show that cranberries can help prevent urinary tract infections and H. pylori infection (a virus which causes ulcers and dental plaque) is ongoing, yet encouraging, according to the National Library of Medicine (MedlinePlus). Cranberries can be found in drinks, teas, as well as in capsules or tablets. While most symptoms associated with cranberry supplements are considered mild, those with some pre-existing conditions or who are taking certain medications should be aware of some safety concerns. It is also important to keep in mind that the FDA does not have strict regulations around herbs or supplements, which means there are no guarantees when it comes to a manufacturer's safety or the strength and effects of its product. 

Stomach Problems 

MedlinePlus recommends drinking 3  to 16 oz. of  cranberry juice twice daily, or between one and six 300  to 400 mg by mouth if taken in pill or capsule form twice  a day. If more than this is taken,  stomach pains and diarrhea  may occur, particularly  in children and adolescents. 

Kidney Stones 

Patients who suffer from nephrolitiasis, better known as kidney stones, should check  with a doctor before taking  cranberry supplements. This is because cranberry, according to zhion.com and MedlinePlus,  contains a high concentration of  the ingredient oxalate, a key ingredient  for kidney stones. 

Blood Thinners 

People  who take blood thinners like warfarin or coumadin should consult with their doctor before taking  cranberry supplements. This is also true if they regularly take aspirin or liver medications. It is believed by some, according to MedlinePlus, that these medications taken together with cranberry can elevate the INR (a blood clotting reading) which can increase the chances for bleeding. 

Complications 

MedlinePlus lists a number of medications that are processed by the kidneys or liver to eliminate waste. The concern is that cranberry supplements may interact with these drugs and/or hamper the organs' ability to process the medications properly. The lists of these medications includes Alzheimer's medications, anthelmintics (to expel worms), antidiabetic, antifungals, antiulcer, cholesterol-lowering drugs, antineoplastics (anticancer agents), antiprotozoals, antiviral agents and clarithromycin. Drugs broken down by the liver include gastrointestinal drugs, diuretics and salicylates like aspirin.